Time-domain and frequency-domain approach to frequency offset correction method for LTE SC-FDMA uplink

Abstract

Systems and methods for canceling carrier frequency offset (CFO) and sampling frequency offset (SFO) in a radio receive chain are disclosed. In one embodiment, a method is disclosed, comprising: receiving a sub-frame via a radio receive chain in a time domain; performing per-user filtering on the sub-frame to obtain a signal for a particular user; obtaining a CFO correction signal; adding the CFO correction signal in the time domain to perform a CFO correction step on the signal for the particular user; performing an FFT on the output of the CFO correction step to obtain samples in a frequency domain; adding an SFO correction signal in the frequency domain to perform an SFO correction to the output of FFT step; and demodulating the output of SFO correction step, thereby performing CFO and SFO correction while reducing inter-carrier interference (ICI).

The invention claimed is: 
     
       1. A method for canceling carrier frequency offset (CFO) and sampling frequency offset (SFO) in a radio receive chain, comprising:
 receiving a sub-frame via a radio receive chain in a time domain; 
 performing per-user filtering on the sub-frame to obtain a signal for a particular user; 
 obtaining a CFO correction signal; 
 adding the CFO correction signal in the time domain to perform a CFO correction step on the signal for the particular user; 
 performing an FFT on an output of the CFO correction step to obtain samples in a frequency domain; 
 adding an SFO correction signal in the frequency domain to perform an SFO correction step on an output of the FFT; 
 demodulating an output of the SFO correction step; and 
 identifying dominant users and performing the CFO correction step for each of the dominant users, 
 wherein the dominant users are users with a high data rate or users with larger frequency offsets, 
 thereby performing CFO and SFO correction while reducing inter-carrier interference (ICI). 
 
     
     
       2. The method of  claim 1 , wherein the sub-frame is a Long-Term Evolution (LTE) single-carrier frequency division multiple access (SC-FDMA) uplink frame. 
     
     
       3. The method of  claim 1 , further comprising determining the CFO correction signal based on a prior sub-frame within a prior frame. 
     
     
       4. A method for canceling carrier frequency offset (CFO) and sampling frequency offset (SFO) in a radio receive chain, comprising:
 receiving a sub-frame via a radio receive chain in a time domain; 
 performing per-user filtering on the sub-frame to obtain a signal for a particular user; 
 determining a CFO correction signal based on a prior sub-frame within a prior frame immediately prior to the received frame, the prior sub-frame having a sub-frame time index equal to a sub-frame time index of the sub-frame, with a sub-frame duration of 1 ms; 
 adding the CFO correction signal in the time domain to perform a CFO correction step on the signal for the particular user; 
 performing an FFT on an output of the CFO correction step to obtain samples in a frequency domain; 
 adding an SFO correction signal in the frequency domain to perform an SFO correction step on an output of the FFT; and 
 demodulating an output of the SFO correction step; 
 thereby performing CFO and SFO correction while reducing inter-carrier interference (ICI). 
 
     
     
       5. The method of  claim 1 , further comprising performing CFO correction steps for each sub-frame using a CFO correction signal based on a prior sub-frame within an immediately prior frame. 
     
     
       6. The method of  claim 1 , wherein obtaining the CFO correction signal further comprises obtaining the CFO correction signal for the particular user from a prior sub-frame. 
     
     
       7. The method of  claim 1 , further comprising obtaining the CFO correction signal based on a time domain, a frequency domain, or a frequency and time domain method. 
     
     
       8. The method of  claim 1 , further comprising obtaining the CFO correction signal without a preamble or pilot symbol. 
     
     
       9. The method of  claim 1 , further comprising obtaining the CFO correction signal with an accuracy of estimation of between 1 ppb and 10 ppb. 
     
     
       10. The method of  claim 1 , further comprising performing CFO correction at both a transmitter and a receiver, thereby enabling a synchronized transmitter and a synchronized receiver. 
     
     
       11. The method of  claim 1 , further comprising performing CFO correction for each of a plurality of users. 
     
     
       12. The method of  claim 1 , further comprising tracking frequency variation due to Doppler frequency variation from a moving mobile user. 
     
     
       13. The method of  claim 1 , wherein the sub-frame is either a Wi-Fi, orthogonal frequency division multiplexing (OFDM), or Long-Term Evolution (LTE) sub-frame, and wherein each transmitting user uses an entirety of a frequency band, and further comprising providing SFO correction at an access point or base station. 
     
     
       14. The method of  claim 1 , further comprising performing ICI correction for ICI error that is not correctable in the frequency domain. 
     
     
       15. The method of  claim 1 , wherein CFO error comprises frequency synchronization error and SFO error comprises phase synchronization error. 
     
     
       16. The method of  claim 1 , further comprising obtaining the CFO correction signal by either a frequency offset estimation method in the time domain, a frequency offset estimation method in the frequency domain, or a frequency offset estimation method in the time domain and in the frequency domain. 
     
     
       17. The method of  claim 1 , wherein obtaining the CFO correction signal further comprises:
 downconverting a received orthogonal frequency division multiplexed (OFDM) signal to baseband; 
 identifying, from the downconverted received signal, a series of OFDM symbols in a time domain; 
 performing a fast Fourier transform (FFT) on a block of several time domain samples to turn the time domain OFDM symbols into frequency domain OFDM symbols, one sample per subcarrier in the received OFDM signal; 
 computing a cross-correlation between in-phase and quadrature samples in each subcarrier and for each frequency domain OFDM symbol, wherein the cross-correlation is computed as a sum of products of either squares or absolute values of the in-phase and quadrature samples; and 
 summing the computed cross-correlation across the series of symbols and across all subcarriers to determine a frequency offset for the received OFDM signal. 
 
     
     
       18. The method of  claim 17 , wherein the received OFDM signal is quadrature amplitude modulation (QAM) modulated and the received OFDM signal is a Wi-Fi, WiMAX, WiGig, or Long Term Evolution (LTE) signal. 
     
     
       19. The method of  claim 17 , further comprising obtaining resource blocks for each user using bandpass filtering on time domain samples, and obtaining frequency offset for each user using the per-user resource blocks. 
     
     
       20. A system, comprising:
 a radio receive chain for receiving an input orthogonal frequency domain multiplexed (OFDM) signal; 
 a baseband processor coupled to the radio receive chain and capable of computing a Fourier transform; and 
 a non-transitory computer-readable medium comprising instructions that, when executed by the baseband processor, cause the system to perform steps comprising: 
 obtaining orthogonal frequency division multiplexed (OFDM) symbols from the input OFDM signal that are in a time domain; 
 performing a Fourier transform on the time domain OFDM symbols to obtain OFDM symbols in a frequency domain; 
 determining a frequency offset based on an estimated correlation between the in-phase signal samples and the quadrature signal samples summed over each subcarrier and summed over each frequency domain OFDM symbol; 
 receiving a sub-frame via a radio receive chain in the time domain; 
 performing per-user filtering on the sub-frame to obtain a signal for a particular user; 
 obtaining a CFO correction signal; 
 adding the CFO correction signal in the time domain to perform a CFO correction step on the signal for the particular user; 
 performing an FFT on an output of the CFO correction step to obtain samples in the frequency domain; 
 adding an SFO correction signal in the frequency domain to perform an SFO correction step on an output of the FFT; and 
 demodulating an output of the SFO correction step, 
 thereby performing CFO correction in the time domain and SFO correction in the frequency domain. 
 
     
     
       21. The system of  claim 20 , further comprising: an antenna for receiving time domain samples; a carrier frequency offset correction module coupled to a time domain portion of the radio receive chain; a fast Fourier transform module coupled to an output of the carrier frequency offset correction module; and a sampling frequency offset correction module coupled to an output of the fast Fourier transform module.